In vitro and in vivo evaluation of terpenoid esters of indomethacin as dermal prodrugs

Cell-Permeable Esterase-Activated Ca(II)-Sensitive MRI Contrast Agent

Calcium [Ca(II)] is a fundamental transducer of electrical activity in the central nervous system (CNS). Influx of Ca(II) into the cytosol is responsible for action potential initiation and propagation, and initiates interneuronal communication via release of neurotransmitters and activation of gene expression. Despite the importance of Ca(II) in physiology, it remains a challenge to visualize Ca(II) flux in the central nervous system (CNS) in vivo. To address these challenges, we have developed a new generation, Ca(II)-activated MRI contrast agent that utilizes ethyl esters to increase cell labeling and prevent extracellular divalent Ca(II) binding. Following labeling, the ethyl esters can be cleaved, thus allowing the agent to bind Ca(II), increasing relaxivity and resulting in enhanced positive MR image contrast. The ability of this probe to discriminate between extra- and intracellular Ca(II) may allow for spatiotemporal in vivo imaging of Ca(II) flux during seizures or ischemia where large Ca(II) fluxes (1-10 μM) can result in cell death.

Establishing a minimal erythema concentration of methyl nicotinate for optimum evaluation of anti-inflammatories

Topical administration of chemicals such as methyl nicotinate that induce erythema have been employed to measure the effectiveness of formulations containing anti-inflammatory agents. Prior studies have utilized a single concentration of methyl nicotinate, between 36.5 and 100 mM, for all test subjects in evaluations of topical formulations. However, individuals have different thresholds of response to methyl nicotinate; thus, a single concentration may not be appropriate for all individuals and could result in the apparent lack of anti-inflammatory activity of the formulation being evaluated. In the current study, we evaluated the use of a minimal erythema concentration (MEC) of methyl nicotinate, defined as the lowest concentration that produces a complete and even erythema at the test site, compared with a 36.5-mM concentration of methyl nicotinate. Hydroalcoholic gels containing the nonsteroidal anti-inflammatory drug ibuprofen were compared with placebo. Diffuse reflectance spectroscopy was employed to measure differences in cutaneous inflammatory response between the control (placebo)-treated group and the ibuprofen-treated group. When chemical erythema was induced using an MEC of methyl nicotinate, greater reductions in erythema were seen in ibuprofen-treated sites compared with sites treated with a 36.5-mM concentration of methyl nicotinate. In conclusion, for an accurate assessment method of erythema induced by methyl nicotinate, consideration should be given to determining the extent of response of an erythema-producing agent on an individual basis. An MEC of methyl nicotinate should be determined and employed for each individual to obtain more consistent and reliable efficacy results of anti-inflammatory activity.

Antiallergic and antihistaminic effect of two extracts of Capparis spinosa L. flowering buds

The antiallergic properties of two lyophilized extracts obtained from Capparis spinosa L. flowering buds (capers) by methanol extraction, carried out at room temperature (CAP-C) or with heating at 60 degrees C (CAP-H), were investigated. The protective effects of CAP-H and CAP-C, orally administered (14.28 mg[sol ]kg), were evaluated against Oleaceae antigen challenge-induced and histamine-induced bronchospasm in anaesthetized guinea-pigs. Furthermore, the histamine skin prick test was performed on humans, applying a gel formulation containing 2% CAP-C (the only extract able to protect against histamine-induced bronchospasm) on the skin for 1 h before histamine application and monitoring the erythema by reflectance spectrophotometry. The CAP-H showed a good protective effect against the bronchospasm induced by antigen challenge in sensitized guinea-pigs; conversely, a significant decrease in the responsiveness to histamine was seen only in CAP-C pretreated animals. Finally, the CAP-C gel formulation possessed a marked inhibitory effect (46.07%) against histamine-induced skin erythema. These two caper extracts displayed marked antiallergic effectiveness; however, the protective effect of CAP-H was very likely due to an indirect mechanism (for example, inhibition of mediator release from mast cells or production of arachidonic acid metabolites); conversely, CAP-C is endowed with direct antihistaminic properties. The different mechanisms of action of CAP-H and CAP-C may be related to a difference in the extraction procedure and, thus, in their qualitative[sol ]quantitative chemical profile.

Ketorolac amide prodrugs for transdermal delivery: stability and in vitro rat skin permeation studies

Various amide prodrugs of ketorolac were synthesized and their rat skin permeation characteristics were determined. The solubility of the prodrugs in propylene glycol (PG) was determined at 37 degrees C while lipophilicity was obtained as 1-octanol/water partition coefficient (logP) and capacity factor (k') using HPLC. Stability of the prodrugs in rat skin homogenate, plasma and liver homogenate was investigated to observe the enzymatic degradation. Rat skin permeation characteristics of the prodrugs saturated in PG were investigated using the Keshary-Chien permeation system at 37 degrees C. The logP value of the prodrugs increased up to 4.28 with the addition of various alkyl chain to ketorolac which has a logP of 1.04. Good linear relationship between logP and capacity factor was observed (r(2)=0.89). Amide prodrugs were converted to ketorolac only in rat liver homogenate. However, the skin permeation rate of amide prodrugs did not significantly increase, probably due to their low aqueous solubility. Chemical modification of the ketorolac amide prodrug and/or the selection of proper vehicle to increase aqueous solubility would be necessary for an effective transdermal delivery of ketorolac.

Ketoprofen 1-alkylazacycloalkan-2-one esters as dermal prodrugs: in vivo and in vitro evaluations

Six new 1-alkylazacycloalkan-2-one esters of ketoprofen (1-6) were synthesized and evaluated as potential dermal prodrugs of ketoprofen. Their lipophilicity by both experimental lipophilicity indices (log k') and calculated ClogP was also determined. In vitro experiments were carried out to evaluate the chemical and enzymatic stability and permeation through excised human skin of these new ketoprofen derivatives. Furthermore, we investigated the in vivo topical anti-inflammatory activity of ester 5, which showed the best in vitro profile, evaluating the ability of this compound to inhibit methyl nicotinate-induced skin erythema on healthy human volunteers. Esters 1-6 showed increased lipophilicity compared with the parent drug (ketoprofen), good stability in phosphate buffer pH 7.4, and were readily hydrolyzed by porcine esterase. Results from in vitro percutaneous absorption studies showed that, among all esters synthesized, only for esters 1 and 5 did a higher cumulative amount of drug penetrate through the skin, compared with that obtained after topical application of ketoprofen. In vivo results showed an interesting delayed and sustained activity of ester 5, compared with the parent drugs.

Liquid crystalline pharmacogel based enhanced transdermal delivery of propranolol hydrochloride

A novel pharmacogel was developed for the enhanced transdermal delivery of propranolol hydrochloride (PH). The synthesized prodrugs, propranolol palmitate hydrochloride (PPH) and propranolol stearate hydrochloride (PSH) self-assembled to form gel simply upon mixing alcoholic solution of prodrug with an aqueous solution in a specified ratio. By varying the ratio of prodrug, alcohol and water, three-component phase diagram was constructed which revealed isotropic-gel-vesicular dispersion regions, respectively concomitant to increasing the ratio of water. The gel phase is termed 'Pharmacogel' and exhibits birefringence under plane-polarized light corroborating the presence of lamellar liquid crystals. The pharmacogel by virtue of high chemical potential gradient and improved physicochemical properties showed the enhanced in-vitro skin permeation flux of 51.5+/-3.7 and 42.5+/-3.1 microg/cm(2)/h from PPH and PSH gel, respectively, as compared to 1.9+/-0.1 microg/cm(2)/h for control; and decrease in lag time (1.8 and 2.8 h for PPH and PSH gel, respectively) compared to control (7.6 h) was observed. The admixing of egg lecithin (EL) in increasing ratio concomitantly decreased the flux values to 31.7+/-2.1 microg/cm(2)/h (at a mole ratio of 50:50 PPH:EL) and increased the lag time. In the gel containing 50% EL, the addition of span 40 and cholesterol slightly reduced the permeation while sodium deoxycholate and Tween-80 improved it. The plasma drug levels following transdermal application of control were low (C(max)=23 ng/ml) while in PPH gel, it increased with time reaching C(max) of 94 ng/ml at 8 h post-application of PPH gel (C(max) of 75 ng/ml at 12 h post application of PL5 gel) and maintained for longer times. The AUC(0-32 h) for PPH gel was much higher (1968 ng h/ml) than control (AUC(0-18 h) was 239 ng h/ml), while EL mixed gel also showed better absorption (AUC(0-32 h) was 1707 ng h/ml). The gel formulations also caused less irritation than control, while mixed gel showed least irritation. This novel self-assembled pharmacogel providing high transdermal permeation with many variables to regulate the delivery is therefore having a great potential in percutaneous delivery.

Estimation of intradermal disposition kinetics of drugs: II. Factors determining penetration of drugs from viable skin to muscular layer

To develop a more efficient transdermal delivery system, it is very important to regulate the intradermal disposition of drugs after topical application. We tried to elucidate the factors determining the intradermal disposition kinetics, especially drug penetration from the viable skin to the muscular layer, mainly based on the six-compartment model, including the contralateral skin and muscle for ten model drugs with different physicochemical characteristics. In vivo transdermal absorption study was performed for six model drugs using the stripped-skin rats. The fitting analyses by the six-compartment model gave the theoretical curves describing the observed data very well and the reasonable pharmacokinetic parameters, showing the pharmacokinetic model should be useful for the estimation of the intradermal disposition kinetics of drugs applied topically again. The simulation study using the pharmacokinetic parameters obtained above could show the relative contribution of the direct penetration and the distribution from the systemic circulation to the muscular distribution of drugs. The largest contribution of direct penetration was observed for antipyrine (90.8%) and the smallest was for felbinac (43.3%). Among the pharmacokinetic parameters obtained above, the clearance from the viable skin to the muscle (CL(vs-m)) was found to be significantly correlated with the unbound fraction of drugs in the viable skin (fu(vs)). Although the clearance from the viable skin to the plasma (CL(vs-p)) also tended to increase as fu(vs) increased, the ratio of CL(vs-m) to CL(vs-p) was significantly correlated with fu(vs), meaning that the larger amount of unbound drug in the viable skin significantly contributes to the direct penetration into the muscle more than to the systemic absorption. On the other hand, k(direct) values obtained in in vitro penetration study-the penetration rate constant of drugs from the viable skin to the muscular layer-were found to be correlated with CL(vs-m) values for seven model drugs. Therefore, adding the in vitro experiments for the other three model drugs, the multiple linear regression analysis of k(direct) was performed for ten model drugs in terms of fu(vs), logarithm of the partition coefficient (Log P) and molecular weight. The results clearly showed the largest and significant contribution of fu(vs) to the direct penetration of drugs from the viable skin to the muscular layer, indicating that a drug with the higher value of fu(vs) in the viable skin can penetrate more into the muscular layer.

New oligoethylene ester derivatives of 5-iodo-2'-deoxyuridine as dermal prodrugs: synthesis, physicochemical properties, and skin permeation studies

Five new oligoethylene ester derivatives (9-13) of 5-iodo-2'-deoxyuridine (IDU) were synthesized and assayed to determine their lipophilicity by both experimental lipophilicity indices (log K') and calculated partition coefficients (CLOGP). In vitro experiments were carried out to evaluate the chemical and enzymatic stability and fluxes through excised human skin of these new IDU derivatives. Esters 9-13 showed increased lipophilicity compared with the parent drug (IDU), had good stability in phosphate buffer (pH 7.4), and were readily hydrolyzed by porcine esterase. No correlation between lipophilicity and skin permeation fluxes of synthesized esters 9-13 was observed. Results from in vitro percutaneous absorption studies showed that, among all esters synthesized, only esters 9 and 10 significantly increased the cumulative amount of IDU that penetrated through excised human skin compared with the parent drug (IDU).

In vitro and in vivo evaluation of polyoxyethylene esters as dermal prodrugs of ketoprofen, naproxen and diclofenac

Novel polyoxyethylene esters of ketoprofen (1(a-e)), naproxen (2(a-e)) and diclofenac (3(a-e)) were synthesized and evaluated as potential dermal prodrugs of naproxen, ketoprofen and diclofenac. These esters were obtained by coupling these drugs with polyoxyethylene glycols by a succinic acid spacer. The aqueous solubilities, lipophilicities and hydrolysis rates of esters 1(a-e), 2(a-e) and 3(a-e) were determined in a buffered solution and in porcine esterase. The permeation of these prodrugs through excised human skin was studied in vitro. Furthermore we investigated the in vivo topical anti-inflammatory activity of esters 1(d), 2(e) and 3(e), which showed the best in vitro profile, evaluating the ability of these compounds to inhibit methyl nicotinate (MN)-induced skin erythema on healthy human volunteers. Esters 1(a-e), 2(a-e) and 3(a-e) showed good water stability and rapid enzymatic cleavage and their hydrolysis rates, both chemical and enzymatic, were not significantly affected by the length of the polyoxyethylenic chain used as promoiety. Concerning in vitro percutaneous absorption studies, only esters 1(d-e), 2(d-e) and 3(c-e) showed an increased flux through stratum corneum and epidermis membranes compared to their respective parent drugs. In vivo results showed an interesting delayed and sustained activity of esters 1(d) and 3(e) compared to the parent drugs. In conclusion polyoxyethylene glycols could prove to be suitable promoieties for ketoprofen, naproxen and diclofenac design since esters 1(d-e), 2(d-e) and 3(c-e) showed some requirements (chemical stability, enzymatic lability and an increased skin permeation) needed to obtain successful dermal prodrugs. Furthermore, was observed an appreciable and sustained in vivo topical anti-inflammatory activity of esters 1(d) and 3(e), compared to the parent drugs, using MN-induced erythema in human volunteers as inflammation model.